Failure Characteristics and Optimization Measures of Weakly Consolidated Sandstone with Rich Water
Open tunnel boring machine(TBM),known for their characteristics such as high speed,low impact,and excellent efficiency,are increasingly being widely applied in underground construction.However,as China intensifies its efforts in developing infrastructure and energy projects in the western regions,construction processes are encountering more and more weakly cemented sandstone formations.The application of open TBM in these formations presents significant challenges,often leading to issues like roof collapses,sidewall instability,and insufficient ground support.To expedite production,the open TBM will be applied worldwide for the first time in the inclined shaft excavation of the Kekegai coal mine.Given the low strength,weak cementation,and high groundwater flow in the Luohe Formation,extensive research has been conducted,building upon previous studies.Various research methods,including field measurements and laboratory tests,were employed to investigate the physical properties,microstructures,mineral composition,water content,and pore structure of the water-rich,weakly cemented sandstone in the Luohe Formation.The test results indicate that the porosity of this formation reaches 25.6％,with strong permeability,and contains approximately 15％clay minerals,suggesting some expansiveness.It is recommended to use ultra-permeable nanometer-grade grouting materials to improve grouting effectiveness.Subsequently,triaxial compression tests were conducted under different moisture content and confining pressure conditions,demonstrating that increasing radial stress has a significant effect on controlling the surrounding rock.Innovative support optimization measures were proposed,including"advance reinforcement+anchor cable mesh+nanometer-grade slurry grouting".Numerical simulations and field applications have shown a significant improvement in rock fragmentation and deformation after optimization,resulting in an increase in the actual excavation rate from 10 m/d to 17 m/d,greatly enhancing excavation efficiency and safety.
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